More commonly we use Lupron to suppress an LH surge but it can be used as a trigger for ovulation. In a natural cycle using no drugs, a follicle develops over about 2 weeks, and then a LH surge causes ovulation. While Lupron causes the anterior pituitary to cease LH secretion, in the first 1-2 days of Lupron use, there is a strong release of LH. That’s why we normally give it early in the cycle, before follicles have developed. Premature ovulation does not occur when we give it early because there are no follicles to ovulate. It is this strong release of LH that makes Lupron a substitute for HCG trigger shot. The quick surge results in a very short blast of LH, which could take place over 1-2 hours. This is very similar to the body’s LH surge that takes place in a natural cycle. After that, the LH has left the system, ovulation occurs 36 hours later, and ovarian stimulation stops. HCG, on the other hand, stays in the body for several days.